This application claims the benefit of Korean No. 2001-47787, filed Aug. 8, 2001, in the Korean Industrial Property office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to an image forming apparatus and method in a laser printer or a photocopying machine, which uses an electrophotographing method, and more particularly, to an image forming apparatus for and method of preventing an image defect, checking a resistance of an image forming roller representing a work environment at a non-image interval and adjusting a quantity of an image light in accordance with the resistance of the image forming roller.
2. Description of the Related Art
Generally, a facsimile, a printer, a photocopying machine or a multi-purpose machine having all functions of the aforementioned three machines through a single apparatus is manufactured commonly to have a printing function. Accordingly, the machines comprise an image forming apparatus for the printing function.
The image forming apparatus is provided with a paper cassette on which a recording medium, e.g., printing paper is stacked. The image forming apparatus picks up and transfers each sheet of printing paper stacked on the paper cassette, and forms visible image on the printing paper transferred in an image forming portion by using toner. Then, the printing paper is discharged after the visible image is formed on the printing paper.
When the image forming apparatus is supplied with power, the image forming apparatus warms up for a predetermined time that is set in accordance with characteristics thereof. When the warming up is completed, the image forming apparatus is in an on-line mode to perform a printing command. If there is no printing command for a predetermined time after the apparatus is in the on-line mode, the image forming apparatus returns to an off-line mode. If the printing command is received in the off-line mode, the image forming apparatus performs a printing operation via the process of warming up. At this point, when the image forming apparatus is supplied with the power or warms up after receiving the printing command in the off-line mode, rollers of a printer engine, which substantially perform the printing operation, are preheated when a predetermined voltage is supplied to the rollers.
However, since each roller of the printer engine is made of conductive rubber material, a resistance of the roller varies according to a work environment of the image forming apparatus. In other words, the resistance of the roller is in inverse proportion to a temperature. Therefore, the resistance of the roller increases when an ambient temperature and humidity of the image forming apparatus are low, and decreases when the ambient temperature and the humidity are high.
The image forming apparatus forms the visible image by depositing the toner on an electrostatic latent image formed in accordance with externally received printing information and transfers the visible image to the printing paper. The roller transfers the visible image to the printing paper by an electric potential difference. At this point, if the resistance of each roller increases, the amount of the toner deposited on the electrostatic latent image is reduced, thereby causing a problem of low density of the visible image. Also, if the resistance of each roller decreases, an amount of the toner deposited on the electrostatic latent image to form the visible image increases, thereby causing a problem of high density of the visible image. Accordingly, there are several problems related to an image development, such as an image contamination of the non-image area, a transfer defect, etc. The problems become more serious in a mono development roller system or a high-speed development system.
Meanwhile, the above conventional image forming apparatus projects a certain quantity of image light in accordance with a predetermined value regardless of the work environment. Thus, there are problems in that the density of the visible image printed on the printing paper decreases when the resistance of the roller developing the visible image on the printing paper increases, and increases when the resistance of the roller decreases.
The object of the present invention to solve the above problems is to provide an image forming apparatus capable of preventing an image defect generated due to an increased or decreased resistance of each roller at a low ambient temperature and humidity or a high ambient temperature and humidity, by checking the resistance representing a work environment at non-image intervals, adjusting a quantity of image light in accordance with the work environment, and improving the quality of printing.
Additional objects and advantageous of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
The above and other objects are accomplished by an image forming apparatus according to the present invention, comprising an electrical charge roller for electrically charging a photosensitive drum, a laser scan unit projecting image light on the photosensitive drum to form an electrostatic latent image corresponding to an input image, a development roller developing the electrostatic latent image formed on the photosensitive drum with toner to form a toner image, a transfer roller rotating in contact with the photosensitive drum and transferring the toner image to a sheet of printing paper when a predetermined voltage is supplied, and a controller controlling the laser scan unit to vary a quantity of the image light projected from the laser scan unit in accordance with a variation of a resistance value of the transfer roller. The controller compensates for a variation of printing density to be compensated by an adjustment of the quantity of the image light projected from the laser scan unit according to the variation of the resistance value.
The controller calculates the resistance value based on a quantity of electricity between the transfer roller and the photosensitive drum. Also, the controller classifies the resistance value into one of a predetermined number of levels by a degree of the variation in the resistance value, and adjusts the quantity of the image light projected from the laser scan unit in accordance with the classified level. Meanwhile, the controller controls the quantity of the image light by adjusting an output level of the laser scan unit and a projection width of the image light.
Meanwhile, the above and other objects are accomplished by a method of controlling image forming operation of the image forming apparatus according to the present invention. The method includes calculating the resistance value of the transfer roller based on a quantity of electricity between the development roller and the photosensitive drum and compensating for the printing density by adjusting the quantity of image light projected from the laser scan unit in accordance with the calculated resistance value.
The method of controlling the image forming operation of the present invention further comprises classifying the calculated resistance value into one of the predetermined number of levels by the degree of the variation in the resistance value. Accordingly, the printing density is compensated for by adjusting the quantity of the image light projected from the laser scan unit in accordance with the classified level.
The printing density is compensated for by adjusting an output level from the image light projected from the laser scan unit and the projection width.
According to the present invention, prior to the printing of the input image, by calculating the resistance value of the transfer roller according to the printing work environment and adjusting the quantity of the image light projected from the laser scan unit in accordance with the variation of the calculated resistance value, a change of the printing density of the toner image printed on the printing paper can be compensated.